The present invention details an antiviral regimen as an approach to the prophylaxis against or treatment of a number of viral infections in mammals using a partially purified viral inhibitor, CVI.
Advances in the pharmacologic treatment of viral infections have been slow in coming and indeed very few efficacious antiviral agents presently exist. Amantadine is showing some success but its activity appears to be limited to the influenza A.sub.2 strains. The antimetabolite antiviral agents, such as Idoxuridine and Cytarabine, are hampered by narrow spectrum of activity and potentially severe side effects. Methisazone is receiving some support for its use against some pox and vaccinia strains, but its use in pox infections is limited to prophylaxis. In general, none of these antiviral agents show any broad spectrum use and are therefore indicated in only a very few cases.
Interferon and interferon inducers represent a new approach to the treatment of viral infections. These agents have led the way into broad spectrum antiviral therapy. Interferon induction, usually mediated by a polyanionic pyran copolymer or double-stranded RNA from a synthetic source, has been shown to promote cellular resistance to a number of viral infections. The use of interferon directly in human beings has shown some promise as well in early clinical trials. Yet, it should be noted that interferon research is still in its infancy and early claims may be shown to have been overly optimistic.
The present invention proposes a new approach to antiviral therapy using a broad spectrum viral inhibitor, designated CVI (contact-blocking viral inhibitor), found in a number of cell types and sources and readily distinguishable from interferon. CVI has been found to be present in the cell culture media of a number of cell and tissue types, including primary and secondary mouse embryo cells, continuous human HeP-2 cells, secondary human lung, and human thyroid cells, (1981, Infect. Immun. 32:449-453; 1981, Infect. Immun. 32:454-457). In the prior publications it has been demonstrated that an antiviral activity was repeatedly present in the culture media (Hanks minimal essential medium supplemented with 10% fetal bovine serum, penicillin-streptomycin, and 0.075% bicarbonate) removed from the various cell lines after a 24 hour incubation period; the antiviral activity was not detectable in culture medium which had not been exposed to cells. This suggests that the antiviral activity is likely produced by the various cells and secreted into the surrounding media.
Quantification and spectrum of the antiviral activity is determined using a microtiter plaque reduction assay (Table 1, footnote b of 32 Infect. Immun. page 450 (1981)). Mouse embryo cultures generally produced the highest levels of inhibitory activity, human lung produced the next highest levels, and human HeP-2, skin-muscle, and thyroid cells produced less activity. Little or no activity was detected in human U amnion and hamster BHK-21 cells.
Broad antiviral activity was demonstrated in vitro against a number of different viruses: vaccinia virus, polio virus type I, herpes simplex virus, sindbis virus, mengo virus, influenza virus and vesicular stomatitis virus. Inhibitory titers of each CVI preparation was dependent on the particular virus that was challenged. CVI isolated from mouse embryo cells shows the highest inhibitory activity against vaccinia virus followed by vesicular stomatitis and polio I viruses whereas antiviral isolates from Human HeP-2 demonstrated a higher activity against polio I virus. Of course, most antiviral substances, as demonstrated in vitro do not correlate with in vivo activity and clinical efficacy.
CVI preparations are also shown to lack cell species specificity of inhibitor action. Inhibitor produced and titered in mouse embryo or human HeP-2 cells are capable of inhibiting vaccinia virus replication in the heterologous species, indicating the absence of a species barrier. Thus, it is not necessary, in contrast to interferon, to produce the inhibitor from cells that are of the homologous species as the one to be treated. The practical implications being that human tissues or human cells in culture will not be necessary for the isolation of a CVI preparation that is active in man.
The problem addressed by the present invention is how this in vitro activity may best be translated into in vivo activity. Thus the present invention provides an effective therapeutic approach to the treatment of viral infections.